package BC125_小乐乐转换成绩;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        if(n>=90 && n<=100) System.out.println('A');
        else if(n>=80 && n<=89) System.out.println('B');
        else if(n>=70 && n<=79) System.out.println('C');
        else if(n>=60 && n<=69) System.out.println('D');
        else if(n>=0 && n<=59) System.out.println('E');
        else System.out.println('F');
    }
}
